The present invention relates to microwave frequency phase shifters, and more particularly to an improved phase shifter which is non-dispersive, and the amount of phase shift is selectable over a predetermined range by an external control signal.
Phase shifters based on the variable capacitance of varactor diodes are commonplace. See, e.g., "Analog Phase Shifter for 8-18 GHz," S. Hopper, Microwave Journal, March 1979, page 48-50. Existing designs are either narrow band, frequency dispersive, have high insertion losses, or are non-reciprocal in operation.
Current procurement trends for airborne radar and electronic warfare equipment stress increasingly wider instantaneous frequency bandwidths for the antenna systems, the limit of which will ultimately be determined strictly by the inventiveness of the industry. At present, it is possible to achieve a 3:1 (115.4%) instantaneous bandwidth using a Rotman lens steered beam array. Rotman lenses are described, for example, in "Wide angle Lens for Line Source Applications," Rotman, W. and Turner, R. F., IEEE Trans. Antennas and Propagation, Vol. AP-11, 1963, pages 623-632. However, the full potential of this antenna system is severely limited, due to the lack of a wideband phase shifter which can angularly resolve the coarse beam steering increment associated with the Rotman lens.